Method for operating a vehicle having a disconnect clutch

Abstract

A method for operating a vehicle that includes a driveline disconnect clutch is described. In one example, the method includes adjusting a pressure of the driveline disconnect clutch as a function of an engine pull-up torque minus a driver demand torque when the pressure of the driveline disconnect clutch is between a torque stroke pressure and a hydraulic stroke pressure.

The invention claimed is: 
     
       1. A vehicle operating method, comprising:
 adjusting a driveline disconnect clutch pressure to a torque stroke pressure via a controller in response to an engine pull-up torque minus a driver demand torque being less than a threshold; and 
 adjusting the driveline disconnect clutch pressure from the torque stroke pressure as a function of the driver demand torque via the controller in response to the engine pull-up torque minus the driver demand torque being less than the threshold and in response to the driver demand torque being less than the engine pull-up torque. 
 
     
     
       2. The method of  claim 1 , where the engine pull-up torque is the driver demand torque at which an engine is requested to be started. 
     
     
       3. The method of  claim 1 , where the torque stroke pressure is a pressure at which an amount of torque transferred through the driveline disconnect clutch is greater than open driveline disconnect clutch drag torque. 
     
     
       4. The method of  claim 1 , further comprising adjusting the driveline disconnect clutch pressure from the torque stroke pressure as a function of the engine pull-up torque. 
     
     
       5. The method as claimed in  claim 1 , further comprising fully closing the driveline disconnect clutch and starting an engine in response to the driver demand torque exceeding the engine pull-up torque. 
     
     
       6. The method of  claim 1 , further comprising commanding fully closing the driveline disconnect clutch and commanding engine starting in response to the engine pull-up torque minus the driver demand torque being less than the threshold and the driver demand torque increasing at a rate that will exceed a torque capacity of an electric machine before an earliest time when the driveline disconnect clutch pressure may reach a hydraulic stroke pressure. 
     
     
       7. The method of  claim 1 , where the driveline disconnect clutch is positioned in a driveline between an engine and an electric machine. 
     
     
       8. A vehicle system, comprising:
 a driveline including an engine and an electric machine; 
 a driveline disconnect clutch positioned in the driveline between the engine and the electric machine; and 
 a controller including executable instructions stored in non-transitory memory to adjust a pressure applied to the driveline disconnect clutch as a function of a difference between an engine pull-up torque and a driver demand torque when the pressure applied to the driveline disconnect clutch is between a first pressure and a second pressure. 
 
     
     
       9. The vehicle system of  claim 8 , where the first pressure is a torque stroke pressure, and where the second pressure is a hydraulic stroke pressure. 
     
     
       10. The vehicle system of  claim 9 , where the torque stroke is a pressure at which an amount of torque transferred through the driveline disconnect clutch is greater than open driveline disconnect clutch drag torque. 
     
     
       11. The vehicle system of  claim 9 , where the hydraulic stroke is a pressure above which a rate of rise of a torque capacity of the driveline disconnect clutch is greater than a threshold rate. 
     
     
       12. The vehicle system of  claim 11 , where the rate of rise of the torque capacity of the driveline disconnect clutch is less than the threshold rate when the pressure applied to the driveline disconnect clutch pressure is between the first pressure and the second pressure. 
     
     
       13. The vehicle system of  claim 8 , further comprising adjusting the pressure applied to the driveline disconnect clutch as a function of a clutch torque capacity when the pressure applied to the driveline disconnect clutch is greater than the second pressure. 
     
     
       14. The vehicle system of  claim 8 , further comprising adjusting the pressure applied to the driveline disconnect clutch to a predetermined pressure in response to the difference between the engine pull-up torque and the driver demand torque being less than a threshold torque. 
     
     
       15. A vehicle operating method, comprising:
 adjusting a driveline disconnect clutch pressure to a torque stroke pressure via a controller in response to an engine pull-up torque minus a driver demand torque being less than a threshold; 
 adjusting the driveline disconnect clutch pressure from the torque stroke pressure as a function of driver demand torque via the controller in response to the engine pull-up torque minus the driver demand torque being less than the threshold and in response to driver demand torque being less than the engine pull-up torque; and 
 adjusting the driveline disconnect clutch pressure from a first pressure to a second pressure and starting an engine via a controller in response to the engine pull-up torque minus a driver demand torque being greater than the threshold and in response to an urgent engine start request. 
 
     
     
       16. The method of  claim 15 , where the urgent engine start request is based on an indication of degradation of an electric machine. 
     
     
       17. The method of  claim 15 , where the urgent engine start request is based on a traffic condition. 
     
     
       18. The method of  claim 15 , where the second pressure is a pressure that fully closes the driveline disconnect clutch. 
     
     
       19. The method of  claim 15 , where starting the engine includes rotating the engine via an electric machine that is coupled to the driveline disconnect clutch. 
     
     
       20. The method of  claim 15 , where the driveline disconnect clutch is positioned in a driveline between an engine and an electric machine.